President George W. Bush walks with President-elect Barack Obama as he arrives for a visit at the White House on Monday. Obama is expected to sign executive orders on stem cell research, emisions, and international family planning.

Washington — In some ways, a president is never more powerful than when he first takes office. He’s just won election, the voters have given him a mandate. And on some issues, when he sits down at that big desk in the Oval Office, all he has to do is wave a magic wand – otherwise known as a pen – to change government policies. No congressional approval is required (at least when money is not involved.)

The flurry of executive orders that President-elect Barack Obama is expected to sign soon after inauguration follows in the modern tradition of American presidents. When partisan control of the White House changes, so does the government’s approach to a range of policies. During the campaign, Mr. Obama signaled areas where he plans immediate changes:

•Stem-cell research. Obama has promised to reverse restrictions on federal funding for embryonic stem cell research put in place during President George W. Bush’s first year in office. Mr. Bush’s position sought to satisfy religious conservatives, who objected to open-ended use of stem cells taken from human embryos for research on diseases. Obama is responding to the concerns of scientists who say the existing stem-cell lines are inadequate.

•International family planning. Obama intends to lift the so-called “gag rule” that bans international family-planning groups that receive US funds from discussing abortion as an option. This rule was introduced by President Reagan (then known as the Mexico City policy), and with each subsequent change of partisan control in the White House, the rule has gone – and come back.

•Carbon-dioxide emissions. Obama has said he will reverse the Bush administration’s decision to block California from regulating greenhouse gases from vehicles. Under the Clean Air Act, California had sought to make air-quality standards more aggressive than national regulations, but Bush’s Environmental Protection Agency said it preferred a national approach, not state-by-state. Seventeen states are set to follow California’s lead.

“One of the things he’ll be doing is trying to reward key partisan constituencies,” says Steven Schier, a political scientist at Carleton College in Northfield, Minn. “Stem cell does that, [as does] international abortion policy.”

One area that will be trickier is national security, in which Bush issued orders aimed at fighting the war on terror post-9/11. In theory, there’s a danger that Obama overreaches, moving too far, too fast. But legal experts expect him to move cautiously in this sensitive area.

“Those are extremely delicate, and I’m certain he’ll be very careful with those and not do something peremptory or off the cuff,” says Carl Tobias, a law professor at the University of Richmond.

So far, advisers to Obama’s transition team have reportedly compiled a list of 200 executive orders or administrative actions the new president can carry out soon after taking office.

Meanwhile, the Bush administration continues to promulgate new regulations and orders, meaning Obama’s list could get longer.

But not every Bush administration action Obama objects to can be reversed easily. This past Sunday, on Fox News, Obama transition co-chair John Podesta mentioned the impending sale of leases for land owned by the federal Bureau of Land Management in Utah. Once those leases are sold, it will be hard to reverse.

The land in question, about 360,000 acres, some of which is located near national parks, would be open for oil and gas drilling. Bush administration officials say the drilling would not be environmentally harmful. But Podesta disagrees. “I think that’s a mistake,” he said on Fox.Podesta said Obama has yet to make final decisions in the areas where he would change course.

“But I would say that as a candidate, Senator Obama said that he wanted all the Bush executive orders reviewed, and will decide which ones should be kept, and which ones should be repealed, and which ones should be amended,” Podesta said on Fox.

Long before Obama’s election, interest groups have been working up policy wish lists of what they would like to see an Obama administration undertake.